Abstract

The common thread of this PhD Thesis is the use of sol-immobilised noble metal nanoparticles prepared by a
novel synthetic route, where the addition of the stabilising agent has been avoided.
The first part of the Thesis presents the development of a novel sol-immobilisation route without the addition of stabilisers (e.g., PVA, PVP). A monometallic 1% wt Au/TiO2 and a bimetallic 1% wt AuPd/TiO2 catalysts were prepared and extensively characterised by different techniques in order to gain information including metal loading, nanoparticles morphology and oxidation state of the metals. It has been shown that despite the stabilisers absence, is still possible to obtain materials exhibiting very similar characteristics with respect to the traditional catalysts prepared by PVA and PVP addition. The catalytic activity of the monometallic sample was firstly evaluated for the oxidation of CO (gas -phase) and glycerol (liquid-phase
under basic conditions), whereas the bimetallic was employed for the solvent-free oxidation of benzyl alcohol.
It has been shown that for the liquid phase reactions, samples behave in a very similar manner to the traditional
ones. However, the stabiliser-free catalyst was not active as expected for CO oxidation: reasons for this
behaviour might be related to the nanoparticles size or to the presence of poisonin g species (i.e., chloride) on
the catalyst’s surface.
The second part is focused on the study of glycerol oxidation in basic conditions by using the novel mono
and bimetallic catalysts synthesized stabiliser-free and their comparison in terms of activity and selectivity to
the traditional catalysts synthesized by common stabilising agents PVA and PVP. It has been shown on the first instance that the selectivity towards the main products tartronate and glycerate follows a trend depending on the presence and nature of the stabiliser, with the stabiliser-free samples being more selective towards the former, followed by PVA and PVP. Experiments at short time and using glyceric acid as starting material revealed that the tartronate cannot only arise as product of secondary oxidation of glycerate. Finally, experiments where selected aliquots of PVA and PVP were added during reaction showed that the nature of
the polymer affects the conversion and selectivity. However, the mechanisms involved have not been fully
understood yet.
The third part presents the catalytic activity of a series of Au and AuPd sol-immobilised catalysts for the plasmonic oxidation of glycerol under neutral conditions. It has been shown tha t the catalysts prepared by sol-immobilisation are active under plasmonic conditions. The effect of the presence and nature of the stabilising polymer, the wavelength and time of illumination and of calcination have also been investigated.
The catalytic activity was proven to be related to the plasmonic effect by performing reactions using different
wavelengths of illumination; the nature of the polymer was proven to affect the plasmonic response of the catalyst; stabiliser-free samples activity significantly improved after calcination, likely due to a stro nger
nanoparticle/support interaction. The plasmonic effect has also been observed for a series of 1% wt AuPd/TiO2
catalysts prepared with different Au:Pd ratios, with enhancement in the conversion increasing with the increase
in the gold content.